1. Field of the Invention
The present invention relates to a sensor for detecting a substance that is adsorbed to and/or desorbed from the surface of semiconductor and a method of manufacturing the same. This invention can be applied to a gas sensor and a bio sensor.
2. Related Background Art
Gas sensors and bio sensors of various types have been proposed to detect the presence or absence of a substance and its concentration.
Among such sensors, semiconductor type sensors are adapted to detect a substance, utilizing a metal oxide semiconductor having a property of changing its resistance in response to adsorption or desorption of the substance. Thus, semiconductor type sensors find applications in gas escape alarms and so on. Oxide semiconductors, tin oxide in particular are popularly used for gas sensors. One of the challenges to existing gas sensor elements is selective detection of a gas as an object of detection.
Due to absorption and/or desorption of molecules that are adsorbed to the surface of a metal oxide semiconductor, the width of the depletion layer that is present on the surface of the metal oxide changes as a function of the adsorption or desorption. Thus, metal oxide semiconductor elements that are used in gas sensor elements are mostly devised to detect the change in the electric resistance of the semiconductor element. In the case of tin oxide, for instance, oxygen molecules adsorbed to the surface of tin oxide are removed as a result of a chemical reaction (combustion) of a gas and the oxygen adsorbed to the surface of tin oxide, and consequently the width of the depletion layer is reduced to by turn lower the electric resistance of the tin oxide.
Due to the above-described principle of operation, it is difficult to detect only a target gas in an atmosphere where gases of a plurality of different types that can change the width of the depletion layer coexist when a single metal oxide semiconductor is used.
Therefore, it is an object of the present invention to provide a sensor that can detect only a target gas to be detected.